Dengue fever threatens to invade the 2024 Summer Olympics

Every time the As the Olympics approach, it seems like a different disease is stalking the event. At Rio 2016, it was Zika. At the postponed Tokyo Games, it was Covid. And at the 2024 Paris Olympics this summer? Take your pick. Authorities have been working to contain dengue fever and measles, which have been on the rise in France and many other countries.

During this summer’s Olympics and Paralympics, millions of people from around the world will converge on the host city: French authorities are preparing to welcome more than 15 million visitors to the country. Even for a capital city accustomed to mass tourism — nearly 40 million people visit Paris every year — this is a huge influx of people. Some will bring infectious diseases with them. Others, lacking sufficient immunity, risk catching something during their stay. With dengue fever and measles already a problem in Paris, authorities have been planning how to limit the potential for the Games to become a superspreader event.

“It’s very difficult to limit the epidemic risk when it comes to dengue,” explains Anna-Bella Failloux, a medical entomologist working at the Pasteur Institute in Paris. The virus is transmitted from human to human by mosquitoes, with the culprit in France being the invasive tiger mosquito, Aedes albopictus. The insect is becoming a growing problem as the weather warms, and Europe’s hot summers are creating conditions for the species to thrive. “The eggs are very hardy, and the mosquito’s metabolism speeds up in the heat. The insect becomes an adult earlier and therefore bites earlier too.”

Tiger mosquitoes are not new to France: they arrived in the south in 2004, and have been in Paris since 2015. Originally from Asia, they lay eggs in pockets of standing water, which can hatch weeks later, even after the water has evaporated. This explains how the insect spread to Europe, first arriving in Genoa, Italy, before moving on to France.

Dengue, however, is a more recent problem. With outbreaks of the virus spreading in tropical parts of the world — there have been an estimated 10 million cases worldwide this year, with South America and Southeast Asia badly affected — France has seen a surge in cases. Between January 1 and April 30, 2024, health authorities recorded 2,166 cases, compared with an average of just 128 for the same period in each of the previous five years. Most of this year’s cases have been imported from the French overseas departments of Guadeloupe, Martinique and French Guiana, where epidemics are ongoing, but the European Centre for Disease Prevention and Control has recorded some cases of transmission within Europe this year, including in France.

This points to the risk of having an event that brings together people from all over the world at a time when cases are rising worldwide. If this increases the number of imported cases in Paris, an abundance of tiger mosquitoes has the potential to spread the virus domestically.

For most, an infection is asymptomatic or results in mild, feverish symptoms, but in some the disease becomes more severe and can be fatal. There is no specific treatment for the virus, and few Europeans have immunity from previous exposure. Vaccines have only become available in recent years and are offered only in a small number of high-transmission countries.